Well, IMHO the top three funniest anime of all 
time are (in no specific order):

Dragon Half
Ping Pong Club
and Photon.

These three shows consistently make me laugh my 
patoot off!  Jubei is also good tho XD~~~  Oh, 
Excel Saga is also a real hoot, but off the top 
of my head, the three you see above are my all 
time favorite comedy animes :)

PS:  Oh, cant forget Golden Boy too!